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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have a ruud oil fired furnace robc-112. I'm having issues

Customer Question

I have a ruud oil fired furnace robc-112. I'm having issues with the a/c functioning but the heat side of things wont come on. I can read the schematic pretty well and have replaced the peanut relays mounted to the right and left side of the fan control (old style) bc-44ab-fa-nlc.I'm sorry but I have to give you as much info as possible because this one is funky! Before I played with the relays I had heat and the condenser would come on when making a call for a/c outside but the blower would not come on at the furnace. I also first had no blower control at the thermostat when I put it from auto to the on position. Now I have control over the fan from the thermostat both in the on position and everything is running fine on the a/c side when the thermostat is in the auto position. I also had the beckett a/c ready kit replaced by a local technician who will not come back to the house nor return calls.One last thing. I noticed today that the limit control on the furnace when you pull one wire off the control, the blower goes on??? When I put a jumper on the two leads to the limit control the blower will not come on when a call for heat is made not to mention the oil burner. Help!!!
Submitted: 4 months ago.
Category: HVAC
Expert:  BillyHvac replied 4 months ago.


Depending on age the blower control can be different between 2 different controls. Do you have a circuit board...or a round dial with numbers on the front wall?

Customer: replied 4 months ago.
It is an old style and not a circuit board
Expert:  BillyHvac replied 4 months ago.

ok so on the front there a vertical box with a round dial in it?

Customer: replied 4 months ago.
No, the fan control is mounted on the blower itself flanked to the right and left with relays. It has a small yellow yellow dial on it along with c, r, and g and a relay in the center of the control with common and normally open
Expert:  BillyHvac replied 4 months ago.

that is for cooling and fan and on...there is a heat sense switch for the heating side...There is a 3rd option if the unit is older than 25 years...and that is a simple bimetal fan switch...I can get a pic for you

Expert:  BillyHvac replied 4 months ago.

see this link for the older style fan switch for heat

click here

Customer: replied 4 months ago.
please do...I also have picture
Expert:  BillyHvac replied 4 months ago.

post any pics you have and I can check style and circle parts

Customer: replied 4 months ago.
On the original statement of issue is the exact part number of the fan control.
Expert:  BillyHvac replied 4 months ago.

that is why I ask if you had the circuit board and you said no.

The relays are attached to the circuit when you said no...I went to the older style.

Putting a jumper across the LIMIT will not do anything as the limit is a normally closed contact. Removing the wire from the limit activates the blower as it thinks the switch is open in an overheat state.

Is the only problem at hand the blower not running in heat mode?

The burner fires but trips on limit due to no blower?

Customer: replied 4 months ago.
I'm sorry but I need another technician
Expert:  Phil replied 4 months ago.

Hello,I am a retired mechanical engineer with 56 years in this business. I will go in depth with you, and up to a 6 hour time limit.

All I ask is please select the ***RATING LINK*** at the top of your page before leaving, that is the only way I am credited through the site.

Rating does not affect your charges nor ability to refund if not satisfied. If you can agree to that, lets continue by all means

please attach a close up photo of the furnace wiring diagram that is glued to the inside of the blower access must be well lit and ***exceedingly well focused, I will mark it up with trouble shooting instructions.

Use the attach files link next to your send button to get the photo to me

Customer: replied 4 months ago.
Hello Phil, I will get photo and I appreciate your contacting me . Please allow me a few hours and I will get a clear photo of the wiring diagram. is it possible for you to provide a cell number and I can shoot you a text with the photo on it? If not no big
Expert:  Phil replied 4 months ago.

Its set up for posting photo's to this dialog box. It creates an open record fo answerr quality control purposes.

Customer: replied 4 months ago.
The wiring schematic is faded and yellowed a bit and wont make a good reference. I don't know if you have access to schematic diagrams online but the model is a robf-112qbga949. I am set up with a beckett oil burner and an a/c ready kit (that has been replaced)
Expert:  Phil replied 4 months ago.

Hello again, click here, this is all I could find, Does that wiring diagram on page 28 match your wiring diagram?

We can go from there

Expert:  Phil replied 4 months ago.
Customer: replied 4 months ago.
That is the diagram. Perfect! I will contact you soon to go over this on the phone as that is probably the best way to proceed. I am very sorry this has dragged on. This is very important to me but I am also in the think of an impossible spring season that I just cant keep up with. Thanks very much. I will be in contact later today or Monday to set up a phone call that works with you.Mike
Expert:  Phil replied 4 months ago.

click here please, set the thermostat on heating and up to 90F, then measure the voltage between C and W marked in red....if you do not have 24vac there, fit a jumper wire between R and W as shown in blue. Tell me what you discovered.

We can go from there

Expert:  Phil replied 4 months ago.

That jumper between R and W is just for a brief test, do not leave it in place

click here please, if you do not have 24vac between R and C marked in light blue, check that wire nut circled in red for a bad connection going to C on the fan relay.

If you have 24vac between R and C, fit the jumper shown in green on the fan relay.

take your time, make sure your test probes are making good contact before deciding if there is voltage read or not.

We can go from there, respond in the simplest sentences possible. Avoid mixing comments or speculations or other questions with what you find or do not find. We will get to that in due time.